Fix wxMSW build with wxUSE_DEFERRED_SIZING==0

Don't define BeginRepositioningChildren() and EndRepositioningChildren() at
all in this case instead of defining them as "do nothing" functions because
BeginRepositioningChildren() still needs to return a bool, so the old code
didn't compile and we would need to add another "#else" to fix this -- instead
make it simpler by just not compiling at all in this case.

include/wx/msw/window.h

@@ -61,8 +61,10 @@ public:
     virtual void Raise();
     virtual void Lower();
 
+#if wxUSE_DEFERRED_SIZING
     virtual bool BeginRepositioningChildren();
     virtual void EndRepositioningChildren();
+#endif // wxUSE_DEFERRED_SIZING
 
     virtual bool Show(bool show = true);
     virtual bool ShowWithEffect(wxShowEffect effect,